The present invention relates to an override system for a drive train having hydraulically-operated means such as a slippable clutch for varying torque transmission in the drive train and preferably for apportioning power between different types of driven members. Two examples of adapting a slipping clutch to a drive train are shown in U.S. Pat. No. 3,424,029, issued to J. Horsch et al. on Jan. 28, 1969, and U.S. Pat. No. 3,478,621, issued to L. E. Johnson et al. on Nov. 18, 1969, both of these patents being assigned to the assignee of the present invention.
More specifically, the present invention provides an override control system which is an improvement over application Ser. No. 86,793, now abandoned, entitled "Drive Train With Controlled Slipping Clutch," of A. L. Woody et al., filed on Nov. 4, 1970, and also assigned to the assignee of the present invention. Application Ser. No. 86,793 was abandoned in favor of continuation application, Ser. No. 304,492, now U.S. Pat. No. 3,831,726. That application relates to a control system for apportioning power to engine-driven auxiliary equipment and to a power output member through pressure control of a hydraulically-operated slippable clutch. Such a system contains a manually-controlled regulating valve that is adjustable within a given range to establish an actuating pressure level in the slippable clutch. With a maximum pressure level setting, the slippable clutch remains fully engaged at high engine speeds to deliver maximum power to the power output member. With an intermediate pressure level setting of the regulation valve, the clutch normally slips in a controlled manner to apportion more power to the auxiliary equipment at the expense of power delivery to the power output member. Thus, the operator can select the mode of operation best suited to the instant phase of operation for the drive line.
However, it has been found that the operator normally selects a predetermined and balanced intermediate power delivery setting for a first instant phase of operation of the drive line. To establish a second instant phase of operation immediately thereafter requiring a maximum pressure load setting to the slippable clutch, the operator has heretofore had to quickly manipulate the manually-controlled regulating valve. Since cyclic and repetitive operational situations are common, it is often necessary for the operator to quickly adjust the regulating valve to a sometimes delicate setting in order to return the drive line to the first instant phase of operation. Thus, the aforementioned control system has sometimes been found to require excessive operator hand control at a time when he is busy with other aspects of the operation. The control system of the present invention overcomes this problem by providing a quick and convenient means to changeover between two power-apportioning modes of operation of a slippable clutch drive train.